1. Field of the Invention
The present invention relates to a video endoscope system that photographs images of body cavities using autofluorescence from living tissue to generate image data which is to be used to determine whether the tissue is normal or abnormal. The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-256168 (filed on Aug. 25, 2000) which is expressly incorporated herein by reference in its entirety.
2. Description of the Related Art
Recently, video endoscope system capable of observing fluorescence (autofluorescence) emitted from living tissue irradiated with a predetermined wavelength of excitation light are used. These video endoscope devices comprise a light source devices for emitting both visible light and excitation light that excites living tissue to cause autofluorescence. This excitation light is typically ultraviolet light. The living tissue irradiated with this excitation light emits autofluorescence. The intensity of the fluorescence generated by healthy tissue is stronger than that generated by unhealthy tissue. A video endoscope system of this kind irradiates living tissue with excitation light emitted from a light source device, creates a fluorescent image based on the intensity distribution of autofluorescence emitted from the living tissue to be displayed on a monitor. Note that in this fluorescence image, normal tissue appears bright, while diseased tissue appears dark. An operator observes the fluorescence image and determines portions darker than other portions in the fluorescence image as diseased tissue. However, the dark portions in a fluorescence image do not always indicate diseased tissue. For example, undulant shape of the tissue itself and a forceps projecting from the distal end of the endoscope forms shadows in the body cavity, which are indicated as dark portions in the fluorescent image. Thus, shaded portions are not easily distinguished from diseased portions.
Therefore, a video endoscope system which generates diagnostic images in which diseased areas are distinguished from shaded portions is proposed. A light source device of this video endoscope system sequentially and repeatedly emits green light, blue light, red light, a reference light that is visible light of a predetermined wavelength, and excitation light. The emitted light is guided into the body cavity of a patient through a light guide installed in the video endoscope to irradiate living tissue. An objective optical system installed in the video endoscope forms images of the object from the green light, the blue light, and the red light, respectively, during the period when the light source device emits the green light, during the period when it emits the blue light, and during the period when it emits the red lights. The images are converted into image signals by a CCD installed in the video endoscope. The image signals are synthesized into a color image by a processor of the video endoscope system.
On the other hand, the objective optical system forms a reference image of the object from the reference light during the period in which the light source device emits the reference light. Also, the objective optical system forms an autofluorescence image of living tissue during the period in which the light source device emits the excitation light. These reference and autofluorescence images are converted into image signals by the CCD, and the image signals are input to the processor. The process or subtracts the image signal obtained from the reference light from the image signal obtained from the autofluorescence to extract only portions from which only weak fluorescence is generated due to abnormalities. Furthermore, the processor sets these portions extracted from the fluorescence image signal to a predetermined color and superposes them on the color image to create a diagnostic image. In this diagnostic image, the operator can distinguish diseased portions from the shaded portions and easily recognize the locations of the diseased areas.
The light source device for this video endoscope system will be described in further detail, referring to FIG. 8. The light source device has a first light source 81 for emitting white light and a second light source 82 for emitting light containing the components of the spectra of the excitation light and reference light. A first wheel 83, a first shutter 84, a prism 85, a diaphragm 86, and a condenser lens C are arranged along the optical path of white light emitted from the first light source 81, in order. As shown in FIG. 9A, the first wheel 83 is a disk, with three openings formed along its circumference. These openings are fitted with a green filter 83G, a blue filter 83B, and a red filter 83R to transmit green light, blue light, and red light, respectively. The first wheel 83 is joined to a motor (not shown) and driven to rotate by this motor. The first wheel 83 is disposed at a location where the filters 83G, 83B, and 83R are sequentially inserted into the optical path of the white light emitted from the first light source 81, with its rotation. The white light emitted from the first light source 81 is sequentially converted into green light, blue light, and red light by the filters 83G, 83B, and 83R of the first wheel 83. The converted light advances to the first shutter 84. This shutter 84 can block incident light or allow it to pass therethrough. The light which passed through the first shutter 84 is then transmitted through the first prism 85 and enters the diaphragm 86 which adjusts amount of the light. The light is then converged by the condenser lens C on the proximal end of the light guide 87.
A second prism 88 is disposed on an optical path of light emitted from the second light source 82. The light emitted from the second light source 82 is split into transmitted light and reflected light by the second prism 88. An excitation light filter 89, a second wheel 90, a third prism 91, and a second shutter 92 are arranged along the optical path of the light transmitted through the second prism 88, in order. The light transmitted through the second prism 88 then enters the excitation light filter 89, which extracts and transmits only those components corresponding to the excitation light from the incident light. The transmitted excitation light then enters the second wheel 90. As shown in FIG. 9B, the second wheel 90 is a disk, with one opening formed along its circumference. This opening is fitted with a transparent member to transmit the excitation light. The second wheel 90 is joined to a motor (not shown) and driven to rotate by this motor. The second wheel 90 is disposed at a location where the opening is periodically inserted into the optical path of the excitation light. The excitation light is then transmitted through the third prism 91 and advances to the second shutter 92. The second shutter 92 can block the incident light or allow it to pass therethrough. The light which passed through the second shutter 92 is then reflected by the first prism 85, and thereafter travels along the same optical path as the green light, the blue light and the red light as described above, and finally enters the light guide 87.
A first mirror 93, a reference light filter 94, a third wheel 95, and a second mirror 96 are arranged along the optical path of the light reflected by the second prism 88, in order. The light reflected by the second prism 88 is further reflected by the mirror 93, then enters the reference light filter 94, which extracts and transmits only the components corresponding to the reference light from the incident light. The transmitted reference light then enters the third wheel 95. As shown in FIG. 9C, the third wheel 95 is a disk, with one opening formed along its circumference. This opening is fitted with a transparent member to transmit the reference light. The third wheel 95 is connected to a motor (not shown) and driven to rotate by this motor. The third wheel 95 is disposed at a location where the opening is periodically inserted into the optical path of the reference light. The reference light is then reflected by the second mirror 96, further reflected by the third prism 91, and thereafter travels along the same optical path as the excitation light described above to enter the light guide 87 finally.
The third wheel 95 allows the reference light to pass therethrough only when the second wheel 90 blocks the excitation light. Besides, while the first shutter 84 transmits the green, blue, or red light, the second shutter 92 blocks the excitation light and the reference light. In contrast, while the second shutter transmits the excitation light or reference light, the first shutter 84 blocks the green, blue, and red lights. After the first shutter 84 has passed each of the green light, blue light and red light once, the second shutter 92 passes each of the excitation light and reference light once. Thus, the green light, the blue light, the red light, the excitation light and the reference light are sequentially and repeatedly incident upon the light guide 87. The light incident on the light guide 87 is guided by the light guide 87 itself and emitted toward an object. The object is thus sequentially and repeatedly irradiated by the green light, the blue light, the red light, the excitation light and the reference light.
Thus, in such a video endoscope system, the light source device must sequentially and repeatedly introduce the green light, the blue light, the red light, the excitation light and the reference light into the light guide 87. Accordingly, the optical system of the light source device has a complex configuration, incorporating the above described three prisms. Such a complex optical system attenuates amount of light entering the light guide 87. Since the resulting autofluorescence from living tissue is faint, autofluorescence of the intensity required for observation cannot be obtained without the application of excitation light of a sufficient intensity. The conventional light source device is incapable of emitting excitation light of a sufficient intensity, failing to cause autofluorescence of the required intensity. Further, a complex optical system requires additional manufacturing steps as well as time and labor to align the optical axis of each optical member, making it difficult to keep down product costs.
It is an object of the present invention to provide a video endoscope system including a light source device that can emit various types of irradiating light with a simple configuration.
To attain this object, first aspect of the video endoscope system has a visible light source for emitting visible light, an excitation light source for emitting excitation light that excites living tissue to cause autofluorescence, which is arranged so that the emitted excitation light crosses, at a predetermined intersecting point, to an optical path of the visible light emitted by said visible light source, a light guide for guiding light to irradiate an object, an optical member disposed at the intersecting point to guide the visible light and the excitation light to the light guide along same optical path, a switching mechanism for switching between the visible light and the excitation light to introduce them in to the optical member, an objective optical system for converging the components of light from a surface of the object irradiated with the light guide other than the excitation light, to form an image of the surface of the object, and an imaging device for picking up the image to convert it into an image signal. A processor controls the switching mechanism to alternately and repeatedly introduce the visible light and excitation light into the light guide, generates normal image data on the basis of a portion of the image signal corresponding to a period during which the visible light is introduced into the light guide, generates fluorescence image data on the bases of a portion of the image signal corresponding to a period during which the excitation light is introduced into the light guide, obtains reference image data from said normal image data, extracting a diseased portion on the basis of the reference image data and the fluorescence image data and superimposes the diseased portion on the normal image data to generate diagnostic image data to be displayed as a moving picture.
This configuration enables the reference image data to be obtained from normal image data without a separate optical system emitting the reference light. Therefore, the video endoscope system can generate diagnostic image data on the bases of the reference image data with a simple illumination optical system through which the excitation light does not attenuate.
Note that the switching mechanism may be a prism or a dichroic mirror for coupling the optical path of the visible light and that of the excitation light together, and shutters that can block the visible and the excitation lights respectively. The switching mechanism may alternatively be a switching mirror that is inserted into and retracted from the intersecting point.
Further, second aspect of the video endoscope system according to the present invention has a light source for emitting light containing components of a spectrum of visible light and components of a spectrum of excitation light that excites living tissue to cause autofluorescence, a light guide for guiding light to irradiate an object, a separation device for separating the light emitted from the light source into components of the spectrum of the visible light and the components of the spectrum of the excitation light, a light guiding optical system for separately guiding the visible light and the excitation light so that they cross each other at a predetermined intersecting point, an optical member disposed at the intersecting point to guide the visible light and the excitation light to the light guide, a switching mechanism for switching between the visible light and the excitation light to introduce them into the light guide, an objective optical system for converging those components of light from a surface of the object irradiated with the light guide other than the excitation light to form an image of the surface of the object, and an imaging device for picking up the image to convert it into an image signal. A processor controls the switching mechanism to alternately and repeatedly introduce the visible light and the excitation light into said light guide, generates normal image data on the bases of a portion of the image signal corresponding to a period during which the visible light is introduced into the light guide, generates the fluorescence image data on the bases of a portion of the image signal corresponding to a period during which the excitation light is introduced into the light guide, obtains reference image data from the normal image data, subtracts a diseased portion on the bases of the reference image data and the fluorescence image data, and superimposes the diseased portion on the normal image data to generate diagnostic image data to be displayed as a moving picture.
This configuration allows the visible light and the excitation light to be obtained from light emitted by the single light source, so that the visible light and the excitation light sequentially and repeatedly enters the light guide. The separation device may be a dichroic mirror or a prism.
Further, the visible light may be sequentially converted into green light, blue light, and red light by a wheel inserted into the optical path of the visible light. In this case, the object is sequentially and repeatedly irradiated with the green light, the blue light, the red light and the excitation light. The imaging device then converts an image of the subject, sequentially and repeatedly irradiated with the green light, the blue light, the red light and the excitation light, into an image signal. The processor then processes this image signal to obtain normal image data and a fluorescence image data. The processor may also generate reference image data on the basis of an image signal obtained by the imaging device while the objects is illuminated by the red light.